This invention relates to optical character reading equipment used in the machine reading of documents such as passports, security passes, and the like. These documents usually contain graphic material, alphanumeric symbols and text, some of which is often coded. Much of this data is visible to, and readable by, both the user and an optical character reader; it is also known to include data in a document which is only readable by a suitable optical character reader. It is also known that part or all of the machine readable text need not be visible under ordinary light, requiring a special light source to render it readable.
The majority of the currently available optical character reading equipment uses as the image sensitive device a charge coupled device, or CCD, array; in older equipment other imaging devices, such as orthicon tubes, are used. The document to be read is illuminated with a suitable light source, and a sharp, focussed image is provided at the light sensitive device by a suitable lens system. This image is then converted into an electronic image of part of the document by suitable accompanying electronic devices. For convenience, in this application, this combination of a focussing lens system and a light sensitive device is termed an "imaging device".
This invention is concerned with providing an improved optical character reader which both simplifies existing readers, and also permits the use of relatively low cost standard CCD arrays in the imaging device. This invention provides an optical system whereby, for example, the optical image of a line, or two or three lines, of text is split into two contiguous equal length sections, and at least one of them is then displaced both laterally and vertically to a position above (or below) the other. By careful selection of the length of the two sections, it is then possible to read both of them at once with a standard CCD array.